I realize it's probably a bit premature since nobody has a KPW yet and no "teardown" has been done, but I figure it might be worth talking about already:

The new lighting system is LED which is then fed into the nanoimprinted light guide (basically a flattened out fiber optic cable).

Could it be possible to hack the LED to produce a different light spectrum? (either hw or possibly even sw?). I know that some LED lights that can change colors just have this done at the semiconductor chip level, effectively enabling multiple colors on one led. So maybe it could be possible to physically hack the led electronics to produce a different color (ie, swap out the chip for a differently programmed one?) or could it even be possible to do this only through a software hack?

I would prefer a light color in the more amber part of the spectrum for nighttime reading. In fact, right now I have a battery operated led clip light I use for reading that only produces amber colored light -it is much more comfortable for nighttime reading than white light and also bothers other (possibly sleeping) people much less.

I know we'll have to wait for a proper teardown of the KPW to talk more realistically about this, but I'm guessing some of you out there have a better grasp on current led lighting technology than myself and may be able to provide some theoretical input to this potential KPW light hack?

I doubt that they used RGB leds for the lighting, but if that is the case, it should be pretty easy to change the color. Otherwise if they're monochrome leds it would be quite impossible...
Moreover, the technology used to diffuse light should be quite sensible to the wavelength of the radiation, so it's possible it would not work with a different color.

... Otherwise if they're monochrome leds it would be quite impossible...
Moreover, the technology used to diffuse light should be quite sensible to the wavelength of the radiation, so it's possible it would not work with a different color.

Energy efficient white LEDs as used in this application are really just blue LEDs with a white phosphor coating. Replacing them would require SMT rework skills (which I have), and replacement LEDs in your choice of color that have the same component footprint and power requirements. Different colors have different requirements.

Tri-color LEDs require much more complex driving circuitry, so it is very unlikely that they would be used in this application.

White light is fairly full spectrum, so filtered narrow spectrum (single color) LEDs would work as well as white for their comparative "diffusion" (or light guide propagation) properties in the Paperwhite kindle.

Thanks to everybody for all the answers! -I'll do a tear down when I have more time towards the end of the year and take it from there. Seems like simply adding a color "filter" might be the quickest first experiment for me. The main question I'm left with after reading your input is how effective the light guide can function with specific areas of the spectrum. I work with component level electronics at work, so the prospect of maybe changing out the led hardware is an option I'll keep open...